Buggy code:
public class DodavanjeKorisnika { private Korisnik k ; private KorisnikServis ks ; private String porukaValidacija ; static final Logger logger = Logger . getLogger ( login . class ) ; private Session s ; private GlavniProzorDirektor ref ; private JFrame frmVrti ; private JTextField textField ; private JTextField textField_1 ; private JTextField textField_2 ; private JTextField textField_3 ; private JTextField textField_4 ; public void OtvoriFormu ( ) { } public DodavanjeKorisnika ( Session s , GlavniProzorDirektor ref ) { } private void initialize ( ) { } private String validirajFormu ( JComboBox comboBox ) { porukaValidacija = "" ; Pattern patternIme = Pattern . compile ( "[a-zA-ZĐđŠšČčĆćŽž<seq2seq4repair_space>]{3,}" ) ; if ( ( textField . getText ( ) . equals ( "" ) ) || ( ! ( patternIme . matcher ( textField . getText ( ) ) . matches ( ) ) ) ) porukaValidacija = "Unesite<seq2seq4repair_space>ime<seq2seq4repair_space>korisnika!" ; else if ( ( textField_1 . getText ( ) . equals ( "" ) ) || ( ! ( patternIme . matcher ( textField_1 . getText ( ) ) . matches ( ) ) ) ) porukaValidacija = "Unesite<seq2seq4repair_space>prezime<seq2seq4repair_space>korisnika!" ; else if ( textField_2 . getText ( ) . equals ( "" ) ) porukaValidacija = "Unesite<seq2seq4repair_space>korisničko<seq2seq4repair_space>ime<seq2seq4repair_space>korisnika!" ; else if ( ( textField_3 . getText ( ) . equals ( "" ) ) || ( ! ( validirajBroj ( textField_3 . getText ( ) ) ) ) ) porukaValidacija = "Unesite<seq2seq4repair_space>broj<seq2seq4repair_space>telefona<seq2seq4repair_space>korisnika!\nBroj<seq2seq4repair_space>treba<seq2seq4repair_space>da<seq2seq4repair_space>bude<seq2seq4repair_space>u<seq2seq4repair_space>formatu<seq2seq4repair_space>06xxxxxxx<seq2seq4repair_space>ili<seq2seq4repair_space>03xxxxxxx" ; else if ( ! ( validirajBrojTelefona ( textField_3 . getText ( ) ) . equals ( "" ) ) ) porukaValidacija = validirajBrojTelefona ( textField_3 . getText ( ) ) ; else if ( textField_4 . getText ( ) . equals ( "" ) ) porukaValidacija = "Unesite<seq2seq4repair_space>korisničku<seq2seq4repair_space>šifru<seq2seq4repair_space>korisnika!" ; else if ( ( comboBox . getSelectedIndex ( ) ) == ( - 1 ) ) { porukaValidacija = "Odaberite<seq2seq4repair_space>privilegiju<seq2seq4repair_space>korisnika!" ; } else if ( ( ( textField_2 . getText ( ) . length ( ) ) < 5 ) || ( ( textField_2 . getText ( ) . length ( ) ) > 10 ) ) porukaValidacija = "Korisničo<seq2seq4repair_space>ime<seq2seq4repair_space>mora<seq2seq4repair_space>sadržavati<seq2seq4repair_space>više<seq2seq4repair_space>od<seq2seq4repair_space>5<seq2seq4repair_space>a<seq2seq4repair_space>manje<seq2seq4repair_space>od<seq2seq4repair_space>10<seq2seq4repair_space>znakova!" ; else if ( ks . provjeriDaLiPostojiIstiKorisnik ( textField_2 . getText ( ) ) ) { <START_BUG> porukaValidacija = "Korisničo<seq2seq4repair_space>ime<seq2seq4repair_space>već<seq2seq4repair_space>postoji!" ; <END_BUG> } return porukaValidacija ; } private String validirajBrojTelefona ( String str ) { } private void ocistiKontrole ( ) { } public Boolean validirajBroj ( String broj ) { } }

Fix:
porukaValidacija = "Korisničko<seq2seq4repair_space>ime<seq2seq4repair_space>već<seq2seq4repair_space>postoji!" ;